1. Field of the Invention
The present invention relates to a recovery processing method and unit of an ink jet printing apparatus, and more specifically, to a recovery processing method and unit for detecting whether or not each nozzle of an ink jet print head is in a non-ejection state or a channel miss state and executing a recovery processing of the print head.
2. Description of the Related Art
A rapidly increasing number of ink jet printing apparatuses are based on a method for printing images by operating heaters provided in ink ejecting nozzles filled with ink to rapidly generate bubbles in the nozzles so that the pressure of the bubbles causes the ink to be injected from the tips of the nozzles so as to land on an opposite printing medium. With the printing apparatus based on this method, as time goes by, remaining bubbles after ejection accumulate within the nozzles and gasses dissolved in the ink becomes bubbles which generate within the print head, thereby hindering the ink from being ejected from the nozzles, resulting in inappropriate printing.
It is also known that the ink remaining in the nozzles is fixed to the interior of the nozzles over time to prevent the ink ejection during image printing.
To solve these known problems, the ink jet printing apparatus of this kind performs a recovery operation by forcibly sucking the ink from the nozzles to correct the inappropriate ink ejection.
In the recovery operation, a suction and recovery operation is performed with predetermined timing, such as at power-on, or whether or not suction and recovery is to be carried out can be determined based on an elapsed time which is measured since the preceding recovery operation using a timer.
Since, however, the suction operation involves the discharge of a relatively large amount of ink, the number of suction operations must be minimized in order to restrain useless ink consumption. Additionally, execution of the suction and recovery operation does not always correct the inappropriate ink ejection successfully.
Thus, several detection systems for directly detecting ink droplets ejected from the nozzles have been proposed. Japanese Patent Application Laid-open No. 61-123545(1986) describes the technique of detecting an output signal obtained when the ink droplets ejected from the nozzles impact on a channel miss detector after flying for a specified period of time, thereby determining whether or not a channel miss is occurring. If a channel miss is occurring, this channel miss state, which may be caused by clog or the like, is eliminated by simultaneously purging (sucking) all the ink channels in a print head.
As in the prior art, however, the ink is uselessly consumed if the recovery processing executed after the detection of the nozzle channel miss comprises only suction. As a result, running costs increase and it becomes necessary to increase the volume of a waste ink absorber for retaining sucked ink in the main body of a printer or the like. Consequently, the size and costs of the apparatus must be increased.
The present invention is provided to solve the above problems. It is an object of the present invention to provide a recovery processing method and unit of an ink jet printing apparatus which can detect the channel miss state of the nozzles of the ink jet print head and which can recover, if any nozzle is in the channel miss state, a normal state of this nozzle while minimizing the amount of useless ink.
According to one aspect of the present invention, a recovery processing method of an ink jet printing apparatus for forming images using a print head having a plurality of nozzles for ejecting ink droplets comprises a first step for detecting channel miss states of the plurality of nozzles and a second step for executing at least one of different recovery processes depending on the channel miss states of the plurality of nozzles detected in the first step.
In the first step, the number of nozzles in the channel miss state among the plurality of nozzles may be determined and in the second step, one of the different recovery processes may be executed depending on the result of this determination. In the second step, the recovery process corresponding to the states detected in the first step may be selected from at least two of those recovery processes in a variety of preliminary ejection modes and those recovery processes in a variety of suction modes. Furthermore, the recovery process by the preliminary ejection mode with low ink consumption may be executed when the number of channel miss nozzles is less. Also, the recovery process in the suction mode with recovery performance higher than that in the preliminary mode but with high ink consumption may be executed when the number of channel miss nozzles is more.
According to another aspect of the present invention, a recovery processing unit of an ink jet printing apparatus for forming images using a print head having a plurality of nozzles for ejecting ink droplets comprises a channel miss detecting means for detecting the channel miss state of the plurality of nozzles and a recovery control means for selecting at least one of a plurality of different recovery processes depending on the channel miss states of the plurality of nozzles detected by the channel miss detecting means and for executing the selected recovery process.